Date: Tue, 10 Dec 1996 03:34:21 GMT
Server: NCSA/1.4.2
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Last-modified: Thu, 29 Feb 1996 19:28:47 GMT
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<title>Multi-level Queries</title>
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<h1> Multi-Level Queries </h1>
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DEVR provides a dynamic data definition language for modeling image and vision data, which can
be integrated with existing image processing and vision applications. Schema definitions can be
fully interleaved with data manipulation, without requiring recompilation. In addition, DEVR
provides a powerful application programmer's interface that regulates data access and schema
definition, maintains indexes, and enforces type safety and data integrity. <br> <br>

The system supports multi-level queries based on recursive constraint trees. A set of HRS entities
of a given type is filtered through a network of constraints corresponding to the parts, properties,
and relations of that type. Queries can be constructed interactively with a menu-driven interface,
or they can be dynamically generated within a vision application using the programmer's interface.
Query objects are persistent and reusable. Users may keep libraries of query templates, which can
be built incrementally, tested separately, cloned, and linked together to form more complex
queries. 

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